It is known that such a boot must meet a requirement of maximum flexibility, so that it presents only minimal restriction for foot movements, and a requirement for optimal fit of the sole of the boot with that of the foot, in a general manner so as to provide a high degree of stability for the user and, in the specific case of the cross country ski boot, to allow precise control of the ski by the foot.
To mitigate the possibility of ensuring such optimal fit through the intermediary of the upper and the shaft of such a boot, which are essentially flexible, it has already been proposed, for example, in U.S. Pat. No. 3,327,410, to attach in two opposite lateral areas of the boot sole, inside the latter, two straps which affix the boot sole to the foot by clamping the latter, and are independent of the binding and of the shaft of the boot so as not to interfere with their flexibility.
The two aforementioned requirements are thus met.
However, the boot described in U.S. Pat. No. 3,327,410 is not completely satisfactory.
Indeed, it can be noted that the path which the straps follow presents a certain number of problems; for each of the straps, this path comprises, beginning with the lateral area of the boot sole by which said strap is attached to the boot, a first ascending section running along the inside of the boot at the level of the cuneiforms and the scaphoid of a foot housed in this boot, then a second ascending section bypassing the instep, running along the inside of the boot first at the level of the cuneiforms and the scaphoid, on the side of the boot which corresponds to the lateral area of the sole, with which the strap under consideration is attached to this sole, then in front of the tibia on the other side of the boot, and finally, a third section which bypasses the ankle joint running along the inside of the boot at the level of the base of the tibia, to return in front of the instep immediately above the second section. The other strap follows an analogous path beginning with the opposite lateral area of the sole, and successively presents, beginning with this lateral area, a first ascending section running along the inside of the boot at the level of the cuneiforms and the scaphoid, a second ascending section running along the inside of the boot and bypassing the instep first at the level of the cuneiforms, then of the base of the tibia, crossing the second section of the first strap, then a third section, which almost totally bypasses the ankle joint at the level of the base of the tibia, to present in the front thereof an end which the user can fasten as desired to the corresponding end of the other strap to ensure a tightening of these two straps and, by this tightening, place the foot flush against the sole of the boot; the third section of the second strap almost totally covers the third section of the first strap which passes through the third section of the second strap through a slit therein to allow the mutual fastening of the respective ends of the two straps.
Because of tis path, the straps act on the foot, to place it flush against the sole, in an area corresponding to the cuneiforms, the scaphoid, and even the base of the tibia, which causes an oblique pressure to be applied to the foot towards the rear and downward, which further tends to apply the heel towards the rear against the joint between the base of the shaft and the boot sole so as to effectively apply the sole of the foot against the boot sole. Pivoting of the sole with respect to the foot, around the heel, occurs when this type of path is involved, which constitutes an appreciable inconvenience in the practice of all sports, and especially in that of cross country skiing, which requires the most precise possible control of the ski by means of the boot sole.
Moreover, the clamping of the ankle joint at the level of the base of the tibia, i.e., at the level of the tibia-tarsal clamp constitutes an impedance for the user to the extent that the opening of this clamp during extension movements of the foot are restricted; this inconvenience, which is generally appreciable, is quite especially bothersome in cross country skiing in that the extension of the foot constitutes one of the basic maneuvers in this sport.
In addition, the superposition of the respective third sections of the two straps and the need for one of them to cross the other makes it particularly inconvenient and tedious to place the straps around the feet. Moreover, because of this the straps are very long, thus, on the one hand, entailing the risks of tangling or folding thereof inside the boot when it is being put on, and, on the other hand, an appreciable cost for these straps.
Other disadvantages are related to the fact that the boot proposed by U.S. Pat. No. 3,327,410 presents, with the exception of the presence of the straps, a completely conventional structure, characterized especially by the presence of a front opening in the shaft and the upper so that the boot can be put on and taken off, with closing as desired by lacing, entirely independent from the clamping of the foot by the straps. In other words, putting the boot on while the straps are disengaged from each other and the shoe is unlaced requires, after the foot is introduced, first, the positioning of the straps and the mutual fastening thereof around the ankle joint, then the lacing of the boot, while taking the boot off requires first the unlacing of the boot, then the disengagement of the straps before the foot can be removed; putting the boot on and removing it are thus made relatively complicated due to the presence of the straps.
Moreover, the presence of the opening for putting on the boot provided with laces in a front area of the shaft and a major portion of the binding, i.e., in the area which is especially exposed to projections of snow in the case of a cross country ski boot, renders the type of boot proposed by U.S. Pat. No. 3,327,410 virtually unusable for cross country skiing; indeed, the extent is known to which the slightest opening placed in such an area in a cross country ski boot, even if it is simply a hole for the passage of a thread, allows moisture to enter the boot, and thus make this boot impossible to use.